Coated reinforced paper and process for preparing same

ABSTRACT

Coated reinforced papers having excellent mechanical and other characteristics are obtained by coating a net-like support obtained from a longitudinally oriented film of polypropylene consisting essentially of isotactic polypropylene with a composition formed of cellulosic or other fibers, mineral and/or organic fillers and/or pigments, and binders.

0 United States Patent 1 51 3,661,700 Zilio 1 May 9, 1972 [S4] COATEDREINFORCED PAPER AND [56] References Cited PROCESS FOR PREPARING SAMEUNITED STATES PATENTS [72] In entor: Gi nfr n Zlli Mil n. I ly 3,l29,4664/1964 LHommedieu ..l62/l08 x [73] Assignee: Montecatinl Edison S.p.A.,Milan, Italy 2'148'490 2/1939 Mmspaugh 100,436 3/1870 Newton l62/l08{22] Filed: Mar. 18, 1970 [21] App.- No: 20,846 Primary Examiner-HowardR, Caine Attorney-P. Q. Peake and Stevens, Davis, Miller & Mosher [30]Foreign Application Priority Data [57] ABSTRACT 1969 "14323 Coatedreinforced papers having excellent mechanical and other characteristicsare obtained by coating a net-like sup- [52] US. Cl ..l62/l03, 162/i04,ll6622//ll0284, p obtained from a longitudinally oriented m ofpolypropylene consisting essentially of isotactic (5 1] Int. Cl. ..B32b5/20, D21d 3/00 r [58] Field oiSearch ..l62/103, 104, I08, 124pdypmpylenc other fibers, mineral and/or organic fillers and/orpigments, and binders.

8 Claims, No Drawings THE PRIOR ART It is known to reinforce paper bycoating it with compositions based on mineral pigments and binders, orby mixing the mineral pigments and binders with the cellulosic fibersbefore the paper is formed.

In general, the mineral pigments used include kaolin, titaniurn dioxide,talc, zinc sulphide, lithopone, calcium and magnesium oxides andcarbonates, barium sulphate, and the like.

Binders used include, in general, natural, animal or vegetable glues orsynthetic glues, in particular casein, gelatines and the like.

In order to obtain coated papers having particularly glossy surfaces,waxes and soaps, such as, for instance, camauba wax, paraffins and thelike, have been included in the coatings.

It is also known to prepare papers, wholly or partially, from syntheticfibers. For instance, in patents and patent applications originatingwith our group there are described papers and fibrous paper-likestructures consisting of cellulosic fibers reinforced by very shortfibers of a propylene polymer having a fine count.

THE PRESENT INVENTION One object of this invention was to provide a newcoated paper adapted to a variety of uses, and having excellentresistance to stresses of different kinds, such as to tearing, wetting,bursting and so on.

This and other objects of the invention are accomplished by thisinvention in accordance with which a composition consisting ofcellulosic and/or other fibers, mineral and/or organic fillers, andbinders is coated onto a support comprising a special fibrouspolypropylenic material which is net-like and obtained from alongitudinally oriented film of polypropylene consisting essentially ofisotactic macromolecules and having, preferably, a melt index comprisedbetween 0.5 and 20.

The supports can be prepared by starting with a polypropylene film,which may be a blown film, orienting it in the longitudinal direction,and then converting it to a net-like structure. One preferred method foreffecting the conversion consists in cutting up the oriented film, bymeans of rollers fitted with staggered pins. The rollers can be ofthetype specified in the published Japanese Patent Application of M. NiwaNo. 22,048/64, filed May 15, I962. The cutting up of the orientedpolypropylene film can also be effected by means of other processes anddevices ofa similar kind. The oriented polypropylene film may be of anydesired thickness as long as it can be converted in a net likestructure; convenient thickness have been been found to be comprisedbetween 0.001 and 0.4 mm for many uses, and preferably between 0.01 and0.25 mm.

In the net-like structures which are particularly suitable for use inpracticing this invention, the meshes of the net have sides whichmeasure from 0.1 to 3.0 cm.

As indicated, the coating applied to the net-like structures to obtainthe reinforced paper of the invention is formed of a conventionalcomposition which is a mixture of cellulosic and/or other fibers, withmineral and/or organic pigments or fillers, and binding agents.

The coating is applied to the net-like polypropylene support byconventional devices, followed by drying and calandering of the coatedsupport.

The following examples are given to illustrate the invention and are notintended to be limiting.

EXAMPLE I A. Preparation of support A support having a net-likestructure was prepared by extruding polypropylene consisting essentiallyof isotactic polypropylene melt index, 2; residual ash content, 0.00lpercent; residue of extraction with n-heptane, 97 percent), to form afilm, stretching the film in the longitudinal direction, and cutting upthe film longitudinally by means of a roller fitted with staggered pins,to produce a net the meshes of which have sides of 0.2 cm.

B. Preparation of the coating A coating paste was prepared by mixingtogether: 5

sulphite cellulose 3 barium sulphate 2 casein 0. water 50 C. Preparationof the paper Using conventional equipment, the coating paste was applied to both faces of the polypropylene net.

Thereupon the coated support was dried and calandered (with a restingtime on the calender of 5 seconds and a temperature of the calanderrollers of l$5 C).

D. Characteristics weight (g./sq.m.)

longitudinal breaking load (kg./sq.mm.) longitudinal elongation at breakresistance to longitudinal tearing (g./2$p.) bursting pressure(kg./sq.cm.)

EXAMPLE 2 A. Preparation of the support A support having a net-likestructure was prepared by extruding polypropylene consisting essentiallyof isotactic polypropylene melt index 2; residual ash content 0.00lpercent; residue of extraction with n-heptane, 97 percent), to obtain afilm, stretching the film longitudinally, and cutting up 30 thestretched film in a longitudinal direction by means of a roller fittedwith pins arranged in a staggered position, such as to produce a net themeshes of which have sides of0.4 cm.

B. Preparation of the coating A coating paste was prepared by mixingtogether:

sulphite cellulose 2.8 kg. kaolin 2.2 kg. gelatine 0.5 kg. water 50 l.

teristics:

weight (g./sq.mt) l00 longitudinal breaking load (kg/mm) 1.4longitudinal elongation at break (9%) 22 longitudinal tear resistance(g./25y.) 25

bursting pressure (kg./sq.cm.) 1.5

EXAMPLE 3 A. Preparation of the support A support with a net-likestructure was prepared by extruding polypropylene consisting essentiallyof isotactic polypropylene melt index, 0.5; residual ash content, 0.00lpercent; residue of extraction with n'heptane, 97 percent) to obtain afilm, by then subjecting the film to a longitudinal stretching, andfinally by cutting up the film in a longitudinal direction by means ofrollers fitted with staggered pins such as to produce a net the meshesof which have sides of 0.25 cm.

B. Preparation of the coating There was prepared a coating paste byadmixing the following substances:

sulphite cellulose 3.l kg. lithopone [.9 kg. gelatine 0.5 kg. water 50l.

C. Preparation of the coated paper The support, consisting of thepolypropylene net-structure, was coated with the coating paste by meansof a conveyor belt permitting application of the coating to both facesof the support. Thereafter, the treated support was dried and thenpassed through a calander with a resting time in the calander of 5seconds, and temperature of the calander-rollers of 155 C.

D. Characteristics The coated paper thus obtained showed the followingcharacteristics:

weight (g./sq.m.)

longitudinal breaking load (kg/mm!) longitudinal elongation at break(5%) longitudinal tearing resistance [g./25p.) bursting pressure(kg./sq.cm.)

The coating applied to the polypropylene net may contain fibersdifferent from cellulosic fibers, in whole or in part. Artificial orsynthetic fibers can be used, including viscose fibers and fibers ofpropylene homopolymers and copolymers such as fibers of heteroblockcopolymers the macromolecules of which are made up of blocks ofpropylene units and blocks of units of other monomers. particularlyethylene and/or butenel.

Polypropylene consisting essentially of isotactic polypropylene, that isof polypropylene made up of macromolecules having substantiallyisotactic structure, is disclosed in Natta et al. US. Pat. No.3,112,300.

As will be apparent, changes in details may be made in practicing thisinvention without departing from its spirit. There fore, we indent toinclude in the scope of the appended claims all modifications which willbe obvious to those skilled in the art from the description and workingexamples given herein.

What is claimed is:

l. Coated paper and similar fibrous structures consisting of a netobtained from a longitudinally oriented film of polypropylene and acoating on the net formed of a mixture of cellulosic fibers, at leastone member selected from the group consisting of organic and mineralfillers and pigments, and at least one binder.

2. Coated paper and similar fibrous structures according to claim 1,characterized in that the net is obtained from a film of polypropyleneconsisting essentially of isotactic polypropylene and having a meltindex of from 0.5 to 20, the net having meshes the sides of which are ofthe same or different length offrom 0.1 to 3.0 cm.

3. Coated paper and similar fibrous structures according to claim 2, andfurther characterized in that the net is obtained from a blown film ofpolypropylene.

4. Coated paper and similar fibrous structures according to claim 2,further characterized in that the coating contains natural, artificialand synthetic fibers.

5. Coated paper and similar fibrous structures according to claim 2,further characterized in that the binder in the coating is at least onemember selected from the group consisting of natural, animal, vegetableand synthetic glues.

6. Coated paper and similar fibrous structures according to claim 5,further characterized in that the binder is at least one member selectedfrom the group consisting of casein and gelatine.

7. A process for preparing coated paper and similar fibrous structureswhich comprises applying, to both faces of a supporting net obtainedfrom a longitudinally oriented film of polypropylene consistingessentially of isotactic polypropylene, a coating consisting ofcellulosic fibers, at least one member selected from the groupconsisting of mineral and organic fillers and pigments, and at least onebinder, drying the coated net, and passing it through a heated calander.

8. The process according to claim 7, characterized in that the calanderis maintained at a temperature of from about C to about C.

* I I i

2. Coated paper and similar fibrous structures according to claim 1,characterized in that the net is obtained from a film of polypropyleneconsisting essentially of isotactic polypropylene and having a meltindex of from 0.5 to 20, the net having meshes the sides of which are ofthe same or different length of from 0.1 to 3.0 cm.
 3. Coated paper andsimilar fibrous structures according to claim 2, and furthercharacterized in that the net is obtained from a blown film ofpolypropylene.
 4. Coated paper and similar fibrous structures accordingto claim 2, further characterized in that the coating contains natural,artificial and synthetic fibers.
 5. Coated paper and similar fibrousstructures according to claim 2, further characterized in that thebinder in the coating is at least one member selected from the groupconsisting of natural, animal, vegetable and synthetic glues.
 6. Coatedpaper and similar fibrous structures according to claim 5, furthercharacterized in that the binder is at least one member selected fromthe group consisting of casein and gelatine.
 7. A process for preparingcoated paper and similar fibrous structures which comprises applying, toboth faces of a supporting net obtained from a longitudinally orientedfilm of polypropylene consisting essentially of isotactic polypropylene,a coating consisting of cellulosic fibers, at least one member selectedfrom the group consisting of mineral and organic fillers and pigments,and at least one binder, drying the coated net, and passing it through aheated calander.
 8. The process according to claim 7, characterized inthat the calander is maintained at a temperature of from about 150* C toabout 155* C.